1. Field of the Invention
The present invention concerns methods to create an image data set by means of a magnetic resonance (MR) system. Moreover, the present invention concerns correspondingly designed magnetic resonance systems and a corresponding electronically readable data storage medium.
2. Description of the Prior Art
Physical principles of MR imaging—the Nyquist theorem, among other things—are described in “Magnetic Resonance Imaging Physical Principles and Sequence Design”.
DE 44 23 806 C1 describes an MR image acquisition via a series of individual measurements.
US 2007/0080685 A1 discloses MR imaging techniques and a system which operate with ultra-short echo times.
New fields of application in magnetic resonance tomography are offered by an acquisition of MR data with very short echo times (<500 μs). It is thereby possible to show substances or tissue which cannot be shown by means of conventional sequences—for instance a (T)SE sequence (“(Turbo) Spin Echo”) or a GRE sequence (“Gradient Echo”)—since their T2 time is markedly shorter than the echo time and thus a corresponding signal from these substances or tissues has already decayed at the point in time of acquisition. For example, with echo times in the range of the corresponding decay time, it is possible to show bones, teeth or ice in an MR image even though the T2 time of these subjects is in a range from 30-80 μs.
Sequences are known that enable a very short echo time. In addition to the radial UTE sequence (“Ultrashort Echo Time”) there is the approach to scan k-space at points in that the free induction decay (FID) is detected. Such a method is also designated as single point imaging since essentially only one raw data point or, respectively, k-space point in k-space is detected per RF excitation.
One example of such a method for single point imaging is the RASP method (“Rapid Signal Point (RASP) Imaging”, O. Heid, M. Deimling, SMR, 3rd Annual Meeting, Page 684, 1995). According to the RASP method, a raw data point in k-space whose phase was coded by gradients is read out at a fixed point in time after the RF excitation relative to the “echo time” TE. The gradients are modified by means of the magnetic resonance system for each raw data point or measurement point and k-space is thus scanned point-by-point, as is shown in FIGS. 1a and 1b herein.